A so-called indirect AC power converting circuit is generally used as the typical main circuitry of an inverter. In the indirect AC power converting circuit, AC is rectified and is converted into DC via a smoothing circuit, whereby an AC output is obtained by a voltage-source converter.
Meanwhile, as a mode of directly obtaining an AC output from an AC voltage, there is known a direct AC power converter represented by a matrix converter. The direct AC power converter does not require a large capacitor for smoothing a voltage ripple due to commercial frequency or a reactor, and thus a converter is expected to be miniaturized. Accordingly, in recent year, a direct AC power converter has been drawing attention as the next generation of a power converter.
For example, Japanese Patent Application Laid-Open No. 2007-312589 and WO 2007/123118 disclose that AC is directly converted into AC without providing a smoothing circuit in a DC link. Further, Japanese Patent No. 4049189 discloses the technology of providing a clamp circuit in a DC link, to thereby solve a problem of regenerative current in a direct AC power converter.
Japanese Patent Application Laid-Open No. 2009-95149 discloses the technology of providing a current-limiting resistor between an input end and a converter, to thereby generate an inrush current flowing into a capacitor of a clamp circuit. Further, after the capacitor is charged with a voltage, a current-limiting resistor is short-circuited by a switch for avoiding power consumption in the current-limiting resistor.
Japanese Patent No. 3772898 discloses the technology of providing series body composed of a diode, a resistor and a capacitor in a DC link in a single-phase capacitorless inverter. This resistor functions as a current-limiting resistor that suppresses an inrush current from flowing into the capacitor.
Note that Japanese Patent No. 3806872, Japanese Patent Application Laid-Open No. 05-56682 (1993) and Japanese Patent No. 2524771 are related to the present application. Japanese Patent No. 3806872 discloses the technology of reducing errors in estimating a rotating position of a motor by causing the current to be supplied to be large and have a lagging phase. Japanese Patent Application Laid-Open No. 05-56682 (1993) discloses the technology of handling instantaneous stop/reactivation of a power source in an indirect AC power converting circuit. Japanese Patent No. 2524771 describes power conversion by means of a diode bridge equivalent to a natural commutation mode of a converter. The technology related to the present invention is also disclosed in Rie Itoh and Isao Takahashi, “Decoupling Control of Input and Output Reactive Power of the Matrix Converter”, IEEJ Technical Meeting on Semiconductor Power Converter, SPC-01-121, 2001, Koji Kato and Jun-ichi Itoh, “Improvement of Waveform for a Boost type AC/DC/AC Direct Converter”, Year 2007 IEEJ National Convention 4-098, 2007, pp. 153 and 154 and Koji Kato and Jun-ichi Itoh, “Improvement of Waveform for a Boost type AC/DC/AC Direct Converter Focused on Input Current” Year 2007 IEEJ Industry Applied Section Meeting 1-31, pp. 279-282.